GlobeNewswire Inc | Feb 26, 2021 07:30AM EST

February 26, 2021

Trial will evaluate Assemblys core inhibitor candidate, vebicorvir, with Arbutus RNAi therapeutic candidate, AB-729, and standard-of-care NrtI therapy

SOUTH SAN FRANCISCO, Calif., and WARMINSTER, Pa., Feb. 26, 2021 (GLOBE NEWSWIRE) -- Assembly Biosciences, Inc. (Nasdaq: ASMB) and Arbutus Biopharma Corporation (Nasdaq: ABUS) today announced the initiation of a Phase 2 clinical trial of Assembly Bios investigational hepatitis B virus (HBV) core inhibitor candidate, also known as a capsid inhibitor, vebicorvir (VBR), in combination with Arbutus proprietary GalNAc delivered RNAi therapeutic candidate, AB-729, and standard-of-care nucleos(t)ide reverse transcriptase inhibitor (NrtI) therapy for the treatment of patients with chronic HBV infection. The companies announced a clinical collaboration agreement in August 2020.

The randomized, multi-center, open-label Phase 2 clinical trial will evaluate the safety, pharmacokinetics, and antiviral activity of the triple combination of VBR, AB-729 and an NrtI compared to the double combinations of VBR with an NrtI and AB-729 with an NrtI. Approximately 60 virologically-suppressed patients with HBeAg negative chronic HBV are expected to be enrolled across these three treatment arms. Patients will be dosed for 48 weeks with VBR 300 mg orally once daily and AB-729 60 mg subcutaneously every 8 weeks, with a 48-week follow-up period. The primary objective of the trial is to evaluate the safety and tolerability of the triple combination, while secondary objectives of the trial include evaluating the effect of the triple combination in reducing HBV viral biomarkers such as HBV DNA, HBV pgRNA and HBsAg. Additional cohorts may be added in the future to evaluate other patient populations and/or combinations.

We are excited to move forward with our collaborators in this proof-of-concept Phase 2 clinical trial designed to evaluate multiple complementary mechanisms of action. Importantly, this trial supports our long-standing belief that multi-drug combinations will be needed to provide patients with chronic hepatitis B a much needed and durable functional cure, stated Gaston Picchio, PhD, Chief Development Officer at Arbutus. We believe reducing HBsAg will be a key component of future HBV curative therapies. AB-729, Arbutus lead HBV asset, has demonstrated competitive HBsAg reductions and a favorable safety and tolerability profile in an ongoing Phase 1b clinical trial, and we are gratified to have it progress in this combination trial.

"Our lead core inhibitor candidate, vebicorvir, in combination with standard-of-care NrtI therapy, demonstrates enhanced antiviral activity with a favorable safety profile fueling our belief that core inhibitors will become a central component of finite and curative therapies for patients with HBV, saidLuisa Stamm, MD, PhD, Chief Medical Officer at Assembly Bio. We also believe that exploring multi-drug combinations with complementary mechanisms of action could increase response rates. We look forward to exploring the promise of combination therapies in our work with Arbutus.

AboutVebicorvir, Assemblys Lead HBV Core InhibitorAssembly Bios HBV portfolio includes three clinical-stage small molecule candidates, all of which are HBV core inhibitors that target multiple steps of the HBV replication cycle. In Phase 2 clinical trials, first-generation core inhibitor vebicorvir (VBR) administered with nucleos(t)ide analogue reverse transcriptase inhibitor (NrtI) therapy demonstrated a favorable safety profile and led to greater viral suppression of both HBV DNA and HBV pgRNA than NrtI therapy alone. VBR is advancing in multiple Phase 2 combination studies.

About Arbutus AB-729AB-729 is an RNA interference (RNAi) therapeutic targeted to hepatocytes using Arbutus novel covalently conjugated N-acetylgalactosamine (GalNAc) delivery technology that enables subcutaneous delivery. AB-729 inhibits viral replication and reduces all HBV antigens, including hepatitis B surface antigen in preclinical models. Reducing hepatitis B surface antigen is thought to be a key prerequisite to enable reawakening of a patients immune system to respond to the virus. Based upon clinical data generated thus far in an ongoing single- and multi-dose Phase 1a/1b clinical trial, AB-729 has demonstrated positive safety and tolerability data and meaningful reductions in hepatitis B surface antigen.

About HBVChronic hepatitis B virus (HBV) infection is a debilitating disease of the liver that afflicts approximately 270 million people worldwide with up to 90 million people inChina, as estimated by theWorld Health Organization. HBV is a global epidemic that affects more people than hepatitis C virus (HCV) and HIV infection combinedwith a higher morbidity and mortality rate. HBV is a leading cause of chronic liver disease and need for liver transplantation, and up to one million people worldwide die every year from HBV-related causes.

The current standard of care for patients with chronic HBV infection is life-long suppressive treatment with medications that reduce, but do not eliminate, the virus, resulting in very low cure rates. There is a significant unmet need for new therapies to treat HBV.

About Assembly BiosciencesAssembly Bio is a clinical-stage biotechnology company committed to bringing finite and curative therapies to the 270 million people living with hepatitis B virus (HBV) worldwide. A pioneer in the development of a new class of potent, oral core inhibitor drug candidates, Assembly Bios approach aims to break the complex viral replication cycle of HBV to free patients from a lifetime of therapy. Assembly Bios strategy toward cure includes a leading portfolio of more potent, next-generation core inhibitors, proof-of-concept combination studies and a research program focused on the discovery of novel HBV targets. For more information, visitassemblybio.com.

About ArbutusArbutus Biopharma Corporation is a publicly traded (Nasdaq: ABUS) biopharmaceutical company primarily dedicated to discovering, developing and commercializing a cure for people with chronic hepatitis B virus (HBV) infection. The Company is advancing multiple drug product candidates that may be combined into a potentially curative regimen for chronic HBV infection. Arbutus has also initiated a drug discovery and development effort for treating coronaviruses (including COVID-19). For more information, visitwww.arbutusbio.com.

Assembly Bios Forward-Looking StatementsThe information in this press release contains forward-looking statements that are subject to certain risks and uncertainties thatcould cause actual results to materially differ. These risks and uncertainties include: Assembly Bios ability to initiate andcomplete clinical trials involving its HBV therapeutic product candidates, including trials contemplated by Assembly Bios clinicalcollaboration agreements, in the currently anticipated timeframes; safety and efficacy data from clinical studies may not warrantfurther development of Assembly Bios product candidates; clinical and nonclinical data presented at conferences may notdifferentiate Assembly Bios product candidates from other companies candidates; continued development and commercializationof Assembly Bios HBV product candidates, if successful, in the China territory will be dependent on, and subject to, Assembly Bioscollaboration agreement governing its activity in the China territory; Assembly Bios ability to maintain financial resourcesnecessary to continue its clinical trials and fund business operations; any impact that the COVID-19 pandemic may have on Assembly Bios business and operations, including initiation and continuation of itsclinical studies or timing of discussions with regulatory authorities; and other risks identified from time to time in Assembly Biosreports filed with the U.S. Securities and Exchange Commission (the SEC). You are urged to consider statements that includethe words may, will, would, could, should, might, believes, hopes, estimates, projects, potential, expects, plans, anticipates,intends, continues, forecast, designed, goal or the negative of those words or other comparable words to be uncertain andforward-looking. Assembly Bio intends such forward-looking statements to be covered by the safe harbor provisions contained inSection 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, asamended. More information about Assembly Bios risks and uncertainties are more fully detailed under the heading Risk Factorsin Assembly Bio's filings with the SEC, including its most recent Annual Report on Form 10-K, Quarterly Reports on Form 10-Qand Current Reports on Form 8-K. Except as required by law, Assembly Bio assumes no obligation to update publicly anyforward-looking statements, whether as a result of new information, future events or otherwise.

Arbutus Forward-Looking StatementsThis press release containsforward-looking statementswithin the meaning of the Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934, and forward-looking information within the meaning of Canadian securities laws (collectively, forward-looking statements).Forward-looking statementsin this press release include statements about the anticipated trial design of Assembly Bios and Arbutus Phase 2 clinical trial; expectations regarding the timing and number of patients enrolled in the Phase 2 clinical trial; the expected dosing of the Phase 2 clinical trial; the possibility of including additional cohorts under the collaboration agreement; the potential for multi-drug combinations to provide patients with chronic hepatitis B a much needed and durable functional cure; and expectations regarding the safety and efficacy of Arbutus product candidates.

With respect to theforward-looking statementscontained in this press release, Arbutus has made numerous assumptions regarding, among other things: the effectiveness and timeliness of the Phase 2 clinical trial with Assembly, and the usefulness of the data; the continued demand for Arbutus and Assemblys assets; and the stability of economic and market conditions. While Arbutus considers these assumptions to be reasonable, these assumptions are inherently subject to significant business, economic, competitive, market and social uncertainties and contingencies, including uncertainties and contingencies related to the ongoing COVID-19 pandemic.

Additionally, there are known and unknown risk factors which could cause Arbutus actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by theforward-looking statementscontained herein. Known risk factors include, among others: the Phase 2 clinical trial may be more costly or take longer to complete than anticipated, and may never be completed, or may not generate results that warrant future development; changes in Arbutus or Assemblys strategy regarding its product candidates and clinical development activities; economic and market conditions may worsen; market shifts may require a change in strategic focus; and the ongoing COVID-19 pandemic could significantly disrupt our and/or Assemblys clinical development programs.

A more complete discussion of the risks and uncertainties facing Arbutus appears in Arbutus Annual Report on Form 10-K, Arbutus Quarterly Reports on Form 10-Q and Arbutus continuous and periodic disclosure filings, which are available atwww.sedar.comand atwww.sec.gov. Allforward-looking statementsherein are qualified in their entirety by this cautionary statement, and Arbutus disclaims any obligation to revise or update any suchforward-looking statementsor to publicly announce the result of any revisions to any of theforward-looking statementscontained herein to reflect future results, events or developments, except as required by law.

Assembly Bio ContactsInvestor ContactAssembly BioLauren GlaserSenior Vice President, Investor Relations and Corporate Affairs(415) 521-3828lglaser@assemblybio.com

Media ContactSam Brown Inc.Audra Friis(917) 519-9577ASMBMedia@sambrown.com

Arbutus Contacts Investors and Media:William H. CollierPresident and CEOPhone: 267-469-0914ir@arbutusbio.com

Pam MurphyInvestor Relations ConsultantPhone: 267-469-0914ir@arbutusbio.com